In by-passing type slidable closures, the thickness of the closure panels as well as the spacing between the closure panels and the amount of overlap between the closure panels varies in different installations. Moreover, in the glass-type slidable closures such as are commonly used in showcases, it is difficult to drill or otherwise form mounting holes in the glass panels.
So-called ratchet-type locks are commonly used for locking glass-type closure panels and include a ratchet bar which is clipped to the inner closure panel and a separate lock member which is slidable onto the ratchet bar to engage the edge of the outer closure panel for locking the closure panels in a closed condition. Such ratchet-type locks, however, are not permanently attached to the closure panels and comprise two entirely separate pieces which must be disassembled for unlocking and then reassembled in order to lock the closure panels. This not only makes the use of such ratchet-type locks more difficult and time consuming but also increases the likelihood of loss of one or more of the parts of the lock when they are removed from the panels. Moreover, the chip on type ratchet bars tend to chip the edge of the glass panels during use and, when tempered glass panels are used, chipping of the edge of the glass panel may cause fragmentating of the entire panel.
It has also been proposed to mount a plunger-type lock on a frame member attached to the edges of the sliding glass panels and movable therewith. Such plunger-type locks are in the form of a key operated bolt which is mounted in a lock housing attached to the frame member on the outer panel and the bolt is movable perpendicular to the outer panel into an opening in the frame member on the inner closure panel. Such plunger-type locks can only be mounted on sliding glass panels which have frame members movable therewith and, moreover, require considerable time and skill to drill the frame members and mount the locks. Further, the hole in the inner panel for receiving the plunger must be accurately aligned with the plunger when the doors are closed and this further complicates the problem of mounting the plunger-type locks.